Answer:
Erythrocyte
Explanation:
Erythrocytes, or otherwise called, red-blood cells are responsible for transporting oxygen and carbon dioxide to and from the cells and tissues. The reason for this is because of a protein called hemoglobin. The hemoglobin found in erythrocytes allow for transportation of oxygen + CO2 to and from cells.
Threatened means they are lowering in numbers and nearing to be endangered.
Endangered means they are dangerously close to being extinct
Extinct means there is none of them left in the wild.
I hope this is what you meant.
